The present invention relates to a hypodermic syringe which cannot be re-used and which is safely disposable.
The re-use of hypodermic syringes by drug abusers is a recognized health problem. Accidental injury of health care personnel and others by used and discarded hypodermic, potentially contaminated syringes, also is an important health problem. A great number of hypodermic syringes of the aforementioned kind have been proposed over the last decades. While a number of them seem to solve the technical problems involved in providing a safely disposable singe-use hypodermic syringe, their design might be considerably improved in regard of economy of construction and safety of function.
One object of the present invention is to provide a hypodermic syringe which can be safely disposed and which cannot be used after a single injection.
Another object of the present invention is to provide a hypodermic syringe of the aforementioned kind consisting of as few parts as possible, and which is easily manufactured.
Still another object of the invention is to provide a hypodermic syringe of the aforementioned kind having a negligible dead space.
An additional object of the present invention is to provide a hypodermic syringe of the aforementioned kind in which the bond between the needle and the syringe is not easily accidentally broken and which is resistant to leakage.
Further objects of the present invention will become obvious from the following brief description of the invention, a drawing illustrating a preferred embodiment thereof described in more detail, and the appended claims.
The present invention concerns a disposable hypodermic syringe, comprising:
an outer barrel having a front end wall and an open rear end,
an inner barrel having a front end wall and an open rear end, slidingly disposable in the outer barrel,
a hypodermic needle disposed axially at the front end of the outer barrel so as penetrate its front end wall and being held, at the rear end of the needle, by the front end wall of the inner barrel,
a plunger slidingly disposable in the inner barrel.
The outer barrel comprises means for interlocking with the inner barrel when the latter is in a fully inserted position. The plunger comprises means for releasing the inner barrel from the outer barrel while the plunger interlocks with the inner barrel so as to allow the plunger and the inner barrel to be withdrawn in combination with the hypodermic needle for a distance sufficient to displace the needle into a space formed between the outer barrel and the inner barrel.
In this specification, the terms xe2x80x9cfrontxe2x80x9d, xe2x80x9crearxe2x80x9d, xe2x80x9cforwardxe2x80x9d, xe2x80x9crearwardxe2x80x9d, xe2x80x9cdistalxe2x80x9d, xe2x80x9cproximalxe2x80x9d, etc. retain their conventional meanings. The front (distal) end of the syringe is the end provided with the needle, the rear (proximal) end is the end provided with the plunger.
The bodies of the outer and inner barrel are substantially cylindrical and fit snugly over their entire facing areas. The inner barrel and the outer barrel are made of a polymer material which is somewhat flexible, such as polypropylene.
According to a first preferred aspect of the invention the means for locking the inner barrel to the outer barrel comprise a circumferential slit in the wall of the inner barrel disposed near its rear end and a projection extending in a radial direction inward from the inner wall of the outer barrel so as to be located in the slit. It is preferred for the projection to be disposed at a wall section that is flanked by axially extending slits so as to make the projection easily deflectable in an outward radial direction. Its deflection may be further supported by a cut-out disposed distally of the projection.
According to a second preferred aspect of the invention the means at the plunger for releasing the inner barrel from the outer barrel comprises a finger extending radially from a radial flange of the plunger. The finger is insertable into the slit of the inner barrel is and displaceable in the slit so as to expel the projection. of the outer barrel. The slit is preferably open-ended at one end for insertion of the plunger finger. It is preferred that the finger insertion is by a distal displacement of the plunger. Thus the insertion portion of the slit extends in an axial direction while the remainder of the slit extends in a circumferential direction.
According to a third preferred aspect of the invention the inner barrel comprises means for guiding the plunger so as to allow it to be displaced in an axial direction only. The means for guiding the plunger may comprise pairs of ridges disposed at the inner wall of the inner barrel extending in a radial direction and spaced to receive an axially extending plunger flange or similar guide means between them. When its finger is disposed in the portion of the slit extending circumferentially, the plunger can however only be displaced in a radial direction, except after expelling the projection of the outer barrel from the slit. The circumferential portion of the slit is defined by a tongue. It is furthermore preferred for that tongue to comprise means for preventing rotation of the plunger upon expelling the projection of the outer barrel from the slit. The plunger is preferably made of a substantially stiff polymer material.
According to a fourth preferred aspect of the invention the inner and outer barrels comprise means for preventing their mutual rotation, such as one or several ridges at at least one of the outer wall of the inner barrel or the inner wall of the outer barrel and that are axially insertable in a corresponding number of slits in the outer of the wall of the outer barrel or the inner barrel, respectively, extending from the rear end of the slitted wall.
At their respective front ends the inner barrel and the outer barrel comprise axial channels disposed in line.
According to a fifth preferred aspect of the invention the hypodermic needle comprises, at its proximal end, means for interlocking with a holding portion disposed in the axial channel of the inner barrel. The means preferably comprise a saw-tooth profile, but another locking profile or a threaded profile is equally feasible. It is important that the interlocking means of the needle be easily insertable into the holding portion but that, once the needle is inserted, it cannot be easily withdrawn. The needle is mounted in the female portion of a conventional luer fitting which can be screwed on the male counterpart of the outer barrel. The needle is however mounted in a manner that allows it to be withdrawn from it in a proximal direction against a resistance which is substantially higher than the resistance required for inserting the end portion of the needle into the holding portion of the inner barrel.
Further advantages of the present invention will become evident from a study of a set of drawings illustrating a preferred embodiment of the invention which is described in detail, and from the appended claims.